July 3, 2013

Military Sonar Disrupts Behavior Of Blue Whales

A new study has found whales do not care for the sound of the sonar used by militaries to detect submarines.

Researchers from Duke University in Durham, North Carolina, have observed the behavior of whales as they come into areas where sonar is being used and found these marine mammals may even avoid venturing into new feeding areas when they hear sonar.

The results of this research suggest militaries should refrain from performing sonar operations in known whale habitats so as to not disrupt their diving or eating patterns. This research was funded by the US Navy Chief of Naval Operations Environmental Readiness Division and the US Office of Naval Research and is published in the Proceedings of the Royal Society B.

To measure the effects of sonar on the whales, the researchers first had to track the animals as they swam underwater. The Duke researchers used instruments mounted to non-invasive suction cups and, using a long pole, affixed them to the back of the whales. These instruments recorded acoustic sound and tracked their movements after being subjected to the sounds made by underwater sonar operating at mid-frequency -- between 3.5 and 4 KHz.

"Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced," said Jeremy Goldbogen of Cascadia Research, the lead author of the study.

"But overall the responses are complex and depend on a number of interacting factors." Some of these factors include where the whales were feeding when subjected to sonar frequencies.

For instance, when the whales were feeding in deeper water they stopped eating and either swam faster or left the area altogether. John Calambokidis, one of the project's lead investigators said whale populations are still down due to whaling, but those whales that are alive could be particularly affected by these sonar sounds.

"Blue whales are the largest animals that have ever lived. Populations globally remain at a fraction of their former numbers prior to whaling, and they appear regularly off the southern California coast, where they feed," said Calambokidis.

This area off the southern California coast is where the US military often tests their underwater sonar systems at very loud volumes.

It's been observed before that sonar sounds have some kind of effect on other marine animals. Environmental groups have even sued the US Navy for carrying out sonar tests in whale habitats. Previous studies have also shown these mid-frequencies can affect the swimming patterns of beaked whales so greatly that they end up stranded on the beach.

Though studies have before been conducted to measure the way whales behave when sonar is introduced to their environment, Brandon Southall, an adjunct researcher with Duke says this is the first study of its kind.

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," said Southall. "These findings help us understand risks to these animals from human sound and inform timely conservation and management decisions."